Logo do repositório

Percorrer por autor "Louza, Fábio B."

A mostrar 1 - 2 de 2
  • Coherence as a criterion for multichannel combining low SNR communications in an upwelling environment
    Publication . Louza, Fábio B.; Jesus, Sergio
    This paper presents a study on the impact of temporal (TCOH) and spatial (SCOH) coherence over low SNR communications in an environment with intense upwelling and demonstrates how to use coherence as a criterion to perform multichannel combining. Using low power signals collected in a shallow water experiment, from two independent and different geometry arrays with four hydrophones each, temporal coherence was estimated. Signals whose TCOH was above a threshold were averaged and SCOH between channels were estimated. Bit error rate results showed that SCOH can be used as a criterion to discard noisy and high multipath channels. Multichannel combination based on SCOH indicated that the use of the arrays can increase the processing gain, even if the sensors are just a few wavelengths from each other. Moreover, longer averaging times provided lower BER but reduced the effective bit rate.
    2020Documento de conferência Acesso restrito Ver mais
  • Superimposed training low probability of detection underwater communications
    Publication . Louza, Fábio B.; DeFerrari, Harry A.
    This paper proposes a superimposed training method for low probability of detection underwater acoustic communications. A long pilot sequence was superimposed to the message for equalization and synchronization purposes. A fast Hadamard transform (FHT) estimated the channel impulse response and compressed the pilot energy. A Wiener filter performed equalization. The interference signal was removed using hyperslice cancellation by coordinate zeroing. An inverse FHT decompressed the remaining sequence energy and the message was retrieved. Results from a shallow water experiment presented bit error rates <10-2 for signal-to-noise ratios <-8 dB.
    2020Artigo científico Acesso aberto Ver mais